Axial Compressor for a Gas Turbine Having Passive Radial Gap Control

ABSTRACT

An axial compressor for a gas turbine having passive radial gap control is provided. The axial compressor includes a guide vane support on which guide vanes are fastened so as to be arranged in a ring, wherein the vane tips of the guide vanes lie opposite a wall section. Thermal insulation is attached to the wall section in the section lying opposite the vane tips in order to equalize the expansion behavior of the guide vane support and the wall section, which by themselves react thermally in different manners, wherein the terminal insulation is matched in the heat input delay effect thereof to the wall section and to the guide vane support in such a way that the thermal expansion behavior of the guide vane support and the wall section is at least equalized over time during transient operation of the axial compressor.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the US National Stage of International Application No. PCT/EP2009/065359, filed Nov. 18, 2009 and claims the benefit thereof. The International Application claims the benefits of German application No. 08020995.0 EP filed Dec. 3, 2008. All of the applications are incorporated by reference herein in their entirety.

FIELD OF INVENTION

The invention relates to an axial compressor for a gas turbine having passive radial gap control, with at least one guide vane ring which is fastened to a guide vane carrier and has in each case a plurality of guide vanes, the vane tips of which lie on the hub side, in each case so as to form a radial gap, opposite a rotationally fixedly arranged wall portion reacting thermally more quickly in relation to the guide vane carrier.

BACKGROUND OF INVENTION

A gas turbine has a turbocompressor, for example, in an axial type of construction. The turbocompressor has a casing with stators attached to it and a rotor which is surrounded by the casing. The rotor has a shaft on which the rotor can be driven in rotation. A shaft cover surrounding the shaft is provided, the outer contour of which forms, together with the inner contour of the casing, a flow duct through the turbocompressor. The flow duct has a cross section widening in the flow direction, so that the flow duct is designed as a diffuser.

The rotor has a plurality of rotor stages which are followed in each case by a rotor blade row. Furthermore, the stator has a plurality of guide vane rows which, as seen in the axial direction, are arranged alternately to the rotor blade rows. Conventionally, in compressors, another guide vane row is arranged downstream of the last rotor blade row, as seen in the flow direction, and, thereafter, a follow-up guide vane row.

The guide vane rows have a plurality of vanes which are in case fastened with their outer end to the casing and point with their inner end in the direction of the shaft. Formed on the inner end of the guide vane is a vane tip which lies opposite the shaft cover so as to face the latter. The clearance between the vane tips and the shaft cover is formed as a radial gap which is dimensioned in such a way that, on the one hand, the vane tips do not butt against the shaft cover when the gas turbine is in operation and, on the other hand, the leakage flow occurring through the radial gap when the gas turbine is in operation is as low as possible. This gap must therefore be designed to be as small as possible, so that high efficiency is achieved and also both the full blading potential of the compressor can be utilized and as high a gain in pressure as possible can be achieved in the following diffuser.

The casing of the turbocompressor is of solid construction so that the pressure and temperature stresses when the gas turbine is in operation can be withstood. Furthermore, the casing is designed to be rigid, so that the introduction of load into the casing when the gas turbine is in operation results in only slight deformation of the casing. In contrast to this, the shaft cover is exposed to lower mechanical stresses when the gas turbine is in operation, and therefore the shaft cover is designed to be thinner and less solid than the casing.

Since the shaft cover is designed with smaller wall thicknesses, as compared with the casing, and usually has material properties different from those of the casing, the shaft cover heats up more quickly than the casing having the guide vane rows fastened to it. The result of this is that, during the startup and rundown of the gas turbine, the shaft cover and the casing have a different rate of thermal expansion, and therefore the size of the radial gap changes during the startup and rundown of the gas turbine, the radial gap being temporarily smaller during startup and larger during rundown.

So that the vane tips of the guide vane row do not butt against the shaft cover and damage this when the turbocompressor is in operation, the radial gap is provided with a minimum height dimensioned in such a way that the vane tips virtually never touch the shaft cover in any operating state of the gas turbine, whether stationary or non-stationary. The result of this is that a correspondingly dimensioned radial gap is reserved at the vane tips and leads to a reduction in efficiency of the gas turbine.

Furthermore, the blockage caused by the radial gap leads to a reduction in the main flow component, with the result that the recovery of pressure in the diffuser is reduced and adverse breakaway phenomena may occur.

On the other hand, it is known from DE 199 45 581 A1 to attach in the turbine units of gas turbines air-cooled heat protection shields which lie opposite the tips of the turbine moving blades. What is intended thereby, however, is to keep the introduction of heat from hot gas into the guide ring permanently at a low level, so that the static components used there have a sufficient service life.

Something similar is known from GB 902,645. This specifies a compressor with a rotor, on the circumferential surface of which the tips of guide vanes lie opposite one another. The rotor circumferential surface is provided with an abrasive and easily cutable layer, so that, in the event of possible contact of the guide vane tips with the rotor, an increased introduction of heat is avoided, which would otherwise lead to further damage.

Moreover, U.S. Pat. No. 3,056,579 discloses a compressor in which introduction of heat from the flow medium into the rotor is permanently limited. To limit this, a dome-shaped air-cooled arrangement is provided between two rotor disks.

SUMMARY OF INVENTION

The object of the invention to provide an axial compressor for a gas turbine with passive radial gap control, which has high efficiency, is achieved by means of such an axial compressor having the features of the claims.

The axial compressor according to the invention, with at least one guide vane ring which is fastened to a guide vane carrier and has a plurality of guide vanes, the vane tips of which lie on the hub side, in each case so as to form a radial gap, opposite a rotationally fixedly arranged wall portion reacting thermally more quickly in relation to the guide vane carrier, has, on the wall portion lying directly opposite the vane tip, heat insulation which is coordinated, in terms of its heat introduction delaying action upon the wall portion and upon the guide vane carrier, in such a way that the thermally induced expansion behavior of the guide ring carrier and wall portion is at least brought into line, preferably is virtually identical, over time during the transient operation of the axial compressor.

When the compressor of a gas turbine is in operation, the guide vane carrier or the casing having the guide vane ring fastened to it and the wall portion are in contact with a hot gas stream. During a cold start, the heat insulation, when attached to the wall portion, has the effect that the wall portion is insulated thermally from the hot gas stream. Since no cooling of the wall portion is provided, the wall portion with a heat insulation portion will assume an identical temperature to a wall portion without a heat insulation portion in the stationary state which is established later. As a result, the heat insulation only delays the introduction of heat from the hot gas stream into the wall portion. Thus, by means of the heat insulation, the introduction of heat into the wall portion can be fixed in such a way that both the casing with its guide vane ring and the wall portion have a similar thermal expansion behavior in time, not a different one in time, as in the prior art. As a result, the height of the radial gap is approximately constant over time, as a result of which, for example during the startup of a still cold gas turbine, the wall portion moves approximately synchronously at a constant distance from the vane tip.

The radial gap can therefore be designed with a lower height, without the vane tip butting against the heat insulation when the gas turbine is in operation. High operating reliability of the gas turbine, which has high efficiency, is thereby achieved.

Preferably, the heat insulation may be designed in the form of a segmented ring by the provision of circumferential segments.

The thermally induced radial expansion of the heat insulation is thereby reduced, so that, during the radial movement of the heat insulation, the radial thermal expansion of the wall portion primarily comes into effect.

According to a further advantageous refinement, the heat insulation may have sealing elements which are provided between the circumferential segments.

As a result, the gaps between the circumferential segments are advantageously sealed off, so that the leakage rate through the radial gap is low.

Advantageously, the heat insulation can be fastened to the wall portion. In this case, it is preferable, furthermore, that the heat insulation can be fastened as a ring to the wall portion by a hooking means and/or a screwing means.

The heat insulation can thereby be fastened to the wall portion in a stable way, so that the heat insulation cannot change its position with respect to the wall portion when the gas turbine is in operation.

Instead of a separate heat insulation ring, the heat insulation may also be formed from a heat protection layer which is applied to the wall portion and is in this case preferably ceramic. This affords simple production and simple attachment, even for already operationally stressed axial compressors.

Furthermore, it is preferable that the guide vanes form at least two guide vane rings which lie next to one another and the radial gaps of which are influenced by the heat insulation.

The guide vanes do not have to be fastened to a separate guide vane carrier. It is also possible that the guide vanes are fastened directly to a casing of the axial compressor which is usually also thicker-walled than the respective wall portion.

Since the heat insulation for passive gap control is provided on the last downstream compressor guide vane row and the follow-up guide vane row, the recovery of pressure in the diffuser of the axial compressor is high.

BRIEF DESCRIPTION OF THE DRAWINGS

A preferred exemplary embodiment of an axial compressor according to the invention and of heat insulation according to the invention is explained below by means of the accompanying diagrammatic drawings in which:

FIG. 1 shows a longitudinal section through the outlet region of an axial compressor,

FIG. 2 shows the section A from FIG. 1, and

FIG. 3 shows a longitudinal section according to FIG. 1 with an alternative embodiment of an axial compressor according to the invention.

DETAILED DESCRIPTION OF INVENTION

As is clear from FIG. 1, an axial compressor 1 has a casing 2 which has a casing contour 3 on its inside. Furthermore, the axial compressor 1 has a shaft (not shown) which is covered radially outwardly by a shaft cover 4. Both the shaft cover 4 and the casing contour 3 form a flow duct which is designed as a diffuser 5. Moreover, the axial compressor 1 has a rotor with rotor blading 6, the rotor being connected rigidly in terms of rotation to the shaft.

Stator blading 7 is provided, fastened to the casing 2, and is established upstream of the rotor blading 6. Downstream of the rotor blading 6 is arranged a guide vane cascade 8 and, downstream of this, a follow-up guide vane cascade 9, the guide vane cascade 8 and the follow-up guide vane cascade 9 forming the outflow region of the axial compressor 1. Both the guide vane cascade 8 and the follow-up guide vane cascade 9 are formed by a plurality of stator vanes which extend radially in the axial compressor 1. The stator vanes have a radially outer end and a radially inner end, the stator vanes being fastened at their radially outer end to the casing 2.

Formed in each case at the radially inner end is a vane tip 14 which points toward the center of the shaft. A shaft cover 4 arranged fixedly in terms of rotation lies opposite the vane tips 14, so that a radial gap 10 is followed between the vane tips 14 and the shaft cover 4.

Heat insulation 11 is attached as a heat insulation ring on the shaft cover 4, directly adjacently to the vane tips 14, by screwing, for example. The heat insulation ring 11 extends in the axial direction of the axial compressor 1 both over the guide vane cascade 8 and over the follow-up guide vane cascade 9.

FIG. 2 shows the section A from FIG. 1, the shaft cover 4 and the heat insulation ring 11 being depicted. The heat insulation ring 11 is attached to the shaft cover 4 and comprises circumferential segments 12 distributed over the circumference, so that the heat insulation ring 11 has a segmented set-up. Between the circumferential segments 12 are formed interspaces into which in each case a sealing element 13 is inserted. The sealing elements 13 are introduced, braced, between the circumferential segments 12.

The heat insulation ring 11 is produced from a material and dimensioned geometrically in such a way that the shaft cover 4 is thermally insulated from the diffuser 9 in the region of the guide vane cascade 8 and of the follow-up guide vane cascade 9, so that the thermal expansion behavior of the shaft cover 4 corresponds approximately to that of the casing 2.

When the axial compressor 9 is started up, hot gas flows through the diffuser 5 and is in direct contact both with the casing 2, the guide vane cascade 8 and the follow-up guide vane cascade 9 and with the shaft cover 4. By the heat insulation ring 11 being attached, the shaft cover 4 is not in direct contact with the hot gas in the diffuser 5 in the region of the guide vane cascade 8 and of the follow-up guide vane cascade 9, so that introduction of heat in this region into the shaft cover 4 is reduced. As a result, the thermal expansion rate, in particular during the startup of the axial compressor 1, of the casing 2 with the guide vane cascade 8 and with the follow-up guide vane cascade 9 and of the shaft cover 4 with the heat insulation ring 11 is approximately identical.

As a result, when the axial compressor 1 is in operation, the radial gap 10, which is formed by the clearance between the circumferential margin of the heat insulation ring 11, facing the diffuser 5, and the vane tips 14, becomes approximately constant over time. What is advantageously achieved as a consequence of this is that, during the startup of the axial compressor 1, the radial gap 10 provided may be smaller than would be necessary if the heat insulation ring 11 had not been provided on the shaft cover 4 and the vane tips 14 are to be prevented from butting against the shaft cover 4. The mass flow of the leakage flow through the radial gap 10 can thus be reduced, so that both the efficiency of the axial compressor 1 and the gain of pressure in the diffuser 5 are further improved.

Furthermore, the heat insulation ring 11 has the circumferential segments 12, so that radial thermal expansion of the heat insulation ring 11 is prevented. Coordination in terms of the choice of material and of the geometric dimension of the heat insulation ring 11 with respect to the shaft cover 4 is consequently simple.

FIG. 3, like FIG. 1, also shows a longitudinal section through part of the gas turbine, components identical to FIG. 1 being given the same reference symbols in FIG. 3. However, the heat insulation ring 11 shown in FIG. 1 and fanned from circumferential segments 12 is replaced, as an equivalent solution alternative to FIG. 1, by a heat protection layer 15 applied directly to the wall portion 4. The heat protection layer is, for example, a conventional 

1.-8. (canceled)
 9. An axial compressor for a gas turbine, comprising: a guide vane ring fastened to a guide vane carrier; a plurality of guide vanes; a wall portion; and a heat insulation, wherein vane tips of the plurality of guide vanes lie on a hub side, wherein the vane tips are opposite the wall portion and in between the vane tips and wall portion a radial gap is formed, wherein the wall portion reacts thermally more quickly in relation to the guide vane carrier, wherein a wall cover of the wall portion is configured as a rotationally fixed shaft cover, and wherein heat insulation is provided on the wall portion and delays a heat introduction upon the wall portion and upon the guide vane carrier in such a way that the thermally induced expansion behavior of the guide vane carrier and the wall portion is substantially equalized over time during a transient operation of the axial compressor.
 10. The axial compressor as claimed in claim 9, wherein the heat insulation is designed in the form of a segmented ring using a plurality of circumferential segments.
 11. The axial compressor as claimed in claim 10, wherein the heat insulation includes a plurality of sealing elements which are provided between the plurality of circumferential segments.
 12. The axial compressor as claimed claim 9, wherein the heat insulation is fastenable to the wall portion.
 13. The axial compressor as claimed in claim 12, wherein the heat insulation is fastenable to the wall portion by a hooking means and/or a screwing means.
 14. The axial compressor as claimed in claim 9, wherein the heat insulation is designed as a heat protection layer applied to the wall portion.
 15. The axial compressor as claimed in claim 14, wherein the heat protection layer is a ceramic heat insulation layer.
 16. The axial compressor as claimed in claim 9, wherein the guide ring carrier is designed as a casing.
 17. The axial compressor as claimed in claim 9, wherein the plurality of guide vanes faun at least two guide vane rings which lie next to one another and the radial gaps of which are controlled by the heat insulation. 